Department of Physics , The Ohio State University , Columbus Ohio 43210 , United States.
Program of Biophysics , The Ohio State University , Columbus Ohio 43210 , United States.
J Am Chem Soc. 2020 Feb 26;142(8):3997-4007. doi: 10.1021/jacs.9b13506. Epub 2020 Feb 11.
Water dynamics on the protein surface mediate both protein structure and function. However, many questions remain about the role of the protein hydration layers in protein fluctuations and how the dynamics of these layers relate to specific protein properties. The fish eye lens protein γM7-crystallin (γM7) is found in vivo at extremely high concentrations nearing the packing limit, corresponding to only a few water layers between adjacent proteins. In this study, we conducted a site-specific probing of hydration water motions and side-chain dynamics at nine selected sites around the surface of γM7 using a tryptophan scan with femtosecond spectroscopy and NMR nuclear spin relaxation (NSR). We observed correlated fluctuations between hydration water and protein side chains on the time scales of a few picoseconds and hundreds of picoseconds, corresponding to local reorientations and network restructuring, respectively. These motions are heterogeneous over the protein surface and relate to the various steric and chemical properties of the local protein environment. Overall, we found that γM7 has relatively slower water dynamics within the hydration shell than a similar β-sheet protein, which may contribute to the high packing limit of this unique protein.
蛋白质表面的水动力既介导了蛋白质结构，又调节了其功能。然而，关于蛋白质水合层在蛋白质波动中的作用，以及这些层的动力学与特定蛋白质性质的关系，仍有许多问题尚未得到解答。鱼类眼睛晶状体蛋白γM7-晶体蛋白（γM7）在体内以极高的浓度存在，接近堆积极限，相邻蛋白质之间只有几个水层。在这项研究中，我们使用飞秒光谱和 NMR 核自旋弛豫（NSR）技术，在γM7 表面的九个选定位置进行了针对水合水分子运动和侧链动力学的定点探测。我们观察到在几皮秒到几百皮秒的时间尺度上，水合水分子和蛋白质侧链之间存在相关波动，分别对应于局部重排和网络重构。这些运动在蛋白质表面上具有异质性，与局部蛋白质环境的各种空间和化学性质有关。总的来说，我们发现 γM7 水合壳内的水动力学比类似的β-折叠蛋白慢，这可能有助于解释这种独特蛋白质具有较高堆积极限的原因。
